The field of the invention is that of electrical circuit units, and the invention relates more particularly to an electrical circuit unit having circuit components fired on an electrically insulating substrate of high thermal conductivity to have improved mechanical, electrical and thermal properties when subjected to high voltages and to high temperatures during manufacture and use.
Large area, low cost, electrical circuit units embodying thick and thin film circuit components and the like are frequently proposed for use in high voltage and high temperature circuit applications. Ceramic electrical insulating materials are frequently proposed for use in such circuit units to withstand the high temperatures which are required for firing thick film circuit components in such circuit units. In that regard, an electrical circuit unit of this general type is considered large if a dimension of the ceramic insulating layer in its circuit plane exceeds the thickness of the insulating layer by a multiple of 25 or more. Such circuit units also typically require dissipation of substantial amounts of heat when the circuit units are operated at their intended high voltages. Typically the use of ceramic insulating layers of larger proportions in such electrical circuit units is limited by the mechanical properties of the circuit unit substrates such as the resistance to fracture of the electrically insulating substrate layers when subjected to shock and vibration and the resistance to stresses due to differences in relative thermal expansion of the substrate materials and other circuit components when subjected to high temperature during firing of circuit components or during use, and by the thermal conductivity which is achieved in the circuit units for dissipating heat from the circuit components before heat build-up damages the circuit components. It is also difficult to provide such a ceramic insulating layer of sufficient thickness for high voltage applications on a metal layer of sufficient thickness to provide a larger area circuit unit with sufficient heat-dissipation for high voltage applications in high temperature environments.
Related subject matter is shown in the commonly assigned copending application for U.S. patent, Ser. No. 587,189.